This invention relates generally to concrete finishing machines, and, more particularly, to apparatus for controllably adjusting the pitch of the trowel blades of such machines.
Concrete finishing machines have been used for many years to level and finish large concrete pads. Such machines typically include a rotatable trowel blade assembly having a plurality (e.g., three or four) generally planar trowel blades mounted on trowel arms projecting radially outwardly from a common hub, all of which are rotated by a gasoline-powered engine. The trowel blades rest directly on the concrete surface to be finished and support the machine's entire weight.
Concrete finishing machines typically further include means for controllably pivoting the trowel blades about their respective radial axes, to change their pitch relative to the concrete surface to be finished. Changing the blades' pitch correspondingly changes the proportion of blade surface contacting the concrete surface, such that the machine's weight is supported by a larger or smaller area of the surface. In use, the machine makes several passes over the concrete surface as the concrete hardens, with the blade pitch being specially selected for each pass. In the initial pass, when the concrete is still very wet and plastic, the blade pitch is usually adjusted to be substantially parallel with the concrete surface, thereby lying flat upon it and spreading the machine's weight over a maximum surface area. In subsequent passes, as the concrete hardens and becomes less plastic, the blade pitch is progressively increased, with the pitch used in the final pass sometimes being as much as about 30 degrees.
Improvements in recent concrete formulations have made some concrete slabs include pockets or areas of varying plasticity. In such situations, it is necessary to rapidly adjust the trowel blade pitch in order to produce the desired finish. It is also necessary to adjust the trowel blade pitch when the machine is being moved to an adjacent area where the concrete is at a different stage of hardness. In this situation, which frequently occurs when very large concrete pads are being formed, the blade pitch must be adjusted very rapidly.
In the past, the pitch of the trowel blades was typically adjusted using a thrust collar that pushed downwardly on fingers projecting upwardly from the rear sides of the respective trowel arms. A downward force on the thrust collar is provided by a yoke that is pivotally secured to the machine's frame. A tension cable connects the end of the yoke opposite the pivot point with a screw handle located at the remote end of a machine handle used by the operator to guide and control the machine. Rotation of the screw handle adjusts the yoke's angle, to move the thrust collar up or down a corresponding amount and thereby provide the desired trowel blade pitch.
The trailing edge of each trowel blade, which contacts the concrete surface on which the machine rests, is spaced from the blade's pivot axis. Any change in blade pitch therefore transfers the machine's weight by raising or lowering the machine on the surface. Since the machine is generally quite heavy, usually weighing several hundred pounds, the screw handle used for blade pitch adjustment must have threads with a very small pitch to permit the operator to rotate it conveniently. Consequently, the blade pitch adjustment can be made only very slowly. This has proven to be unsatisfactory in many situations.
Some concrete finishing macines have overcome the slow pitch adjustment afforded by the screw handle described above by replacing the screw handle with a long lever attached to the machine's framework. Although this configuration permits a rapid adjustment of the blade pitch, it is not generally convenient to use. This is because the lever requires large movements for lever advantage and because the lever is not conveniently located on the machine handle itself and thus requires the operator to control the machine using merely one hand and unsteady footing.
It should be appreciated from the foregoing that there is a significant need for a concrete finishing machine having a trowel blade adjustment apparatus that can be used by the operator to rapidly adjust the trowel blade pitch, yet is simple in construction and convenient to use. The present invention fulfills this need.